1. Field of the Invention
The present invention is concerned with an apparatus and method for determining the position of an object. More particularly, the present invention is concerned with a device for aligning the steerable wheels of a vehicle which uses a laser beam source coupled to one steerable wheel, a phototransistor array coupled to the other steerable wheel, and a microcomputer coupled to the array for producing an output signal representative of the relative position of the two wheels compensated for the effects of ambient light, phototransistor bias, and the like.
2. Description of the Prior Art
The prior art discloses systems for determining the position of an object which are particularly useful for the alignment of one steerable wheel of a vehicle relative to another steerable wheel or relative to the centerline of the vehicle frame. In particular, some of these systems for vehicular wheel alignment use beams of visible light, such as laser beams, and an associated photodetector. Such combinations are advantageous in that the use of a light beam eliminates the need for measuring tapes or strings. Photodetectors, however, are subject to undesirable signal bias caused by ambient light, internal photodetector bias, and the like.
U.S. Pat. Nos. 4,150,897, and 4,311,386, which are hereby incorporated by reference, disclose devices which attempt to compensate for photodetector signal bias. Both disclose devices which cause a beam of light to sweep across the area of an associated photodetector to thereby produce a modulated signal which can be filtered from the background signal bias in order to determine the toe angle of the respective steerable wheels of a vehicle. The use of a mechanical device to sweep a beam of light across a beam detector, however, tends to be complex and pre-sents the potential for mechanical failure.
Accordingly, the prior art points out the need for an apparatus for accurately determining the position of an object without the use of a mechanical device to sweep or modulate a beam of light.